With the increased usage of electrical equipment for various applications, the
demand for quality power apart from continuous power availability has increased and
hence requires the development of appropriate power conditioning system. A major
factor during development of these systems is the requirement that they remain
environment-friendly. This cannot be realized using the conventional systems as they
use batteries and/or engine generators. Among various viable technologies, fuel cells
have emerged as one of the most promising sources for both portable and stationary
applications.
In this thesis, a new battery less UPS system configuration powered by fuel cell is
discussed. The proposed topology utilizes a standard offline UPS module and the battery
is replaced by a supercapacitor. The system operation is such that the supercapacitor
bank is sized to support startup and load transients and steady state power is supplied by
the fuel cell. Further, the fuel cell runs continuously to supply 10% power in steady
state. In case of power outage, it is shown that the startup time for fuel cell is reduced
and the supercapacitor bank supplies power till the fuel cell ramps up from supplying 10% load to 100% load. A detailed design example is presented for a 200W/350VA 1-
phase UPS system to meet the requirements of a critical load. The equivalent circuit and
hence the terminal behavior of the fuel cell and the supercapacitor are considered in the
analysis and design of the system for a stable operation over a wide range. The steady
state and transient state analysis were used for stability verification.
Hence, from the tests such as step load changes and response time measurements, the
non-linear model of supercapacitor was verified. Temperature rise and fuel consumption
data were measured and the advantages of having a hybrid source (supercapacitor in
parallel with fuel cell) over just a standalone fuel cell source were shown. Finally, the
transfer times for the proposed UPS system and the battery based UPS system were
measured and were found to be satisfactory. Overall, the proposed system was found to
satisfy the required performance specifications.